The embodiments of the present invention relate to a lower-noise microwave amplifying circuit which is used for a lower-noise converter for satellite broadcast reception use. More particularly, a lower-noise microwave amplifying circuit is presented which is more easily adjusted than in the basic performance of input VSWR (i.e., voltage standing-wave-ratio) or the like and is simpler in construction.
A conventional microwave amplifying circuit for use in such a converter is generally constructed as shown in FIG. 5. FIG. 5 shows a top plan view of the top plan of the conventional converter having the essential portions in this example.
Referring to FIG. 5, in order to adjust the basic performance of the input VSWR or the like, island-shaped patterns 3, 3, . . . are provided near the connecting portion between the input coaxial rod of the coaxial waveguide conversion portion and the microstrip line 2 to connect them properly with the microstrip lines 2 through soldering or the like for the adjusting operation. A semiconductor circuit element 4 is composed of GaAs field effect type transistors (FET) or the like.
The island-shaped patterns 3, 3, . . . provided as described hereinabove have the following disadvantages:
(1) More time, and labor are required to make adjustments, because the respective island-shaped patterns 3, 3, . . . must be soldered in a connecting operation for the adjustment;
(2) A Solder removing operation is very difficult to perform when beginning from start;
(3) A risk is present for electrostatically breaking the semiconductor circuit element 4, such as GaAs FET, etc., in the adjustment;
(4) Fine adjustments are difficult to make, because island-shaped patterns 3, 3, . . . are restricted in size; and
(5) Effects are produced when adjusting the input VSWR and also, influences to the noise figure, and the gain characteristics are produced which deetermine their respective characteristics.